In recent years, in the field of high-speed serial wire communication, research and development on faster communication interfaces is conducted. For example, standardization of high-speed interchip communication interfaces realizing a rate exceeding 10 Gb/s has been started. In high-speed serial communication, transmission-line loss depends on frequency, and inter-symbol interference (ISI) is caused. As a result, an eye pattern at a data reception end of a receiver is distorted. It is known that the bit error rate is increased in such case. This is attributable to the fact that binary transmission is a mainstream trend and a higher data rate is thus achieved by increasing the clock frequency.
To inhibit ISI-related waveform degradation by reducing a transmitted symbol frequency and to improve a data rate, Non-Patent Document 1 discloses an analog multi-tone (AMT) technique as a large-capacity wire transmission method based on frequency division multiplexing using carrier waves.
The transmission system disclosed in Non-Patent Document 1 is an 18 Gb/s level transmission system in which four channels of signals having a 3 Gb/s symbol width are multiplexed and transmitted in three frequency bands. Feed forward equalizers (FFEs) in the transmission circuit include finite impulse response (FIR) filters by digital signal processing. These FFEs execute waveform equalization. In addition, the FFEs execute upconversion to a 3 GHz band and a 6 GHz band on a plurality of baseband signals. In particular, by using two carrier waves having I and Q phases orthogonal to each other in the 3 GHz band, the FFEs multiplex two data in the single frequency band. To multiplex 3 Gb/s symbols on the four channels, the FFEs execute oversampling at a rate four times the 3 Gb/s symbol width and control waveforms at such timing. As illustrated in FIG. 2, as an equalized reception waveform, a 12 Gb/s eye opening is obtained at a symbol rate 3 Gb/s.
Non-Patent Document 1:
A. Amirkhany et al., “A 24 Gb/s Software Programmable Analog Multi-Tone Transmitter,” IEEE Journal of Solid-State Circuits, vol. 43, no. 4, p. 999-1009, April 2008